Exposure information storage device for a photographic camera

Abstract

A storage device for storing photographic exposure information employs a closed-loop analog-to-digital (A-D) converter circuit includes a counter and a digital-to-analog (D-A) converter. The influence of erroneous signals which are created at the output of the D-A converter when the exposure information is stored in the counter is eliminated. The D-A converter circuit employs a ladder network of coarse accuracy. The stored exposure value, however, is highly accurate because of the closed-loop nature of the A-D converter circuit. Means responsive to the stored value for operating the exposure system of the camera are disclosed.

What is claimed is: 
     
       1. An exposure information storage device for a camera capable of storing exposure information supplied thereto comprising: (a) an exposure information producing means for providing an analog value corresponding to a supplied exposure information;   (b) an analog-to-digital converter means, said means including a pulse producing means for providing pulses having a predetermined period, a counter means for counting pulses from said pulse producing means, a digital-to-analog conversion means for converting the content of said counter means into an analog electrical value, a comparator means for comparing the analog value from the exposure information producing means with the analog electrical value from the digital-to-analog conversion means for producing a completion signal when both analog values assume a predetermined relation with each other, said analog-to-digital converter means being responsive to said completion signal so as to terminate the analog-to-digital conversion operation; and   (c) a control circuit coupled to the analog-to-digital converter means, said circuit for controlling the analog-to-digital converter means to avoid responding to the output of the comparator means during the change of the output of the digital-to-analog conversion means caused by the counting of pulses by said counter means.   
     
     
       2. An exposure information storage device for a camera capable of storing the exposure information supplied thereto comprising: (a) an exposure information producing means for providing an analog value corresponding to a supplied exposure information;   (b) a pulse generating means for producing pulses at a predetermined period;   (c) a counter means for counting pulses from the pulse producing means;   (d) a digital-to-analog conversion means responsive to said counter means for providing an analog electrical value representative of the content of the counter;   (e) a comparator means for comparing the analog value from the exposure information producing means with the analog electrical value from the digital-to-analog conversion means, the output of said comparator means being changed from a first signal to a second signal when both analog values reach a predetermined relation with each other;   (f) a transmitting means for transmitting the pulses from the pulse producing means to the counter means in response to the first signal and for prohibiting the transmission of the pulses from the pulse producing means to the counter means in response to the second signal; and   (g) a control circuit coupled to the transmitting means, said circuit for applying an independent signal from the output of the comparator means to the transmitting means corresponding to the first signal for a certain determined time in synchronization with said pulses.   
     
     
       3. An exposure information storage device for a camera capable of storing the exposure information supplied thereto comprising: (a) an exposure information producing means for providing an analog value corresponding to a supplied exposure information;   (b) a pulse generating means for producing pulses at a predetermined period;   (c) a counter means for counting pulses from the pulse producing means;   (d) a digital-to-analog conversion means responsive to said counter means for providing an analog electrical value representative of the content of the counter;   (e) a comparator means for comparing the analog value from the exposure information producing means with the analog electrical value from the digital-to-analog conversion means, the output of said comparator means being changed from a first signal to a second signal when both analog values reach a predetermined relation with each other;   (f) a transmitting means for transmitting the pulses from the pulse producing means to the counter means in response to the first signal and for prohibiting the transmission of the pulses from the pulse producing means to the counter means in response to the second signal; and   (g) a control circuit coupled to the transmitting means for applying a signal corresponding to the first signal to the transmitting means for a predetermined time in synchronism with said pulses independently of the output of the comparator means.   
     
     
       4. An exposure information storage device for a camera in accordance with claim 2 or 3, wherein said control circuit includes a logic circuit having a NAND construction. 
     
     
       5. An exposure information storage device for a camera in accordance with claim 2 or 3, wherein the exposure information producing means includes a light measuring circuit for providing an analog output corresponding to the brightness of the object to be photographed. 
     
     
       6. An analog-to-digital converter circuit for storing an analog input signal supplied thereto comprising: means for providing an analog input signal for storage;   means for providing pulses;   a counter responsive to said pulse providing means for counting pulses;   digital-to-analog conversion means for converting the content of the counter into an analog output signal;   a control circuit for terminating the pulse counting operation of the counter and having a comparator responsive to the analog input signal and the digital-to-analog output signal for providing a completion signal to terminate the pulse counting operation of said counter when said two analog signals are related in a predetermined manner   and a control means to prevent the count stopping operation by the control circuit during changing of the output of the digital-to-analog conversion means at the time of pulse counting by the counter.   
     
     
       7. An analog-to-digital conversion device for a camera comprising: (a) an exposure information producing circuit for providing an analog output corresponding to a supplied exposure information;   (b) a pulse producing circuit for forming pulses;   (c) an analog-to-digital conversion circuit including a counter means for counting the pulses, a digital-to-analog conversion means for converting a content of the counter means into an analog value, detecting means for detecting the analog value and the analog output and producing a signal for stopping the count operation of the counter means when the analog value and the analog output reach a predetermined relation;   (d) preventive means for avoiding the stopping of the count operation with the signal from the detecting means due to temporary changes in the output of the digital-to-analog conversion means during counting by the counter means.   
     
     
       8. An analog-to-digital conversion circuit according to claim 6, wherein the control means nullifies the completion signal from the comparator when changing the output of the digital-to-analog conversion means.